Sarcoidosis is a multisystem, granulomatous inflammatory disease of unknown etiology. Hereditary susceptibility to sarcoidosis is suggested by reports of familial clustering and a higher prevalence in certain ethnic groups, particularly African Americans. Over four hundred kindreds been reported in the medical literature and these investigators have recently described 101 families and shown that African Americans have a higher prevalence rate of familial sarcoidosis than Caucasians (19% vs. 5%). The reasons why sarcoidosis clusters in families or the role of genetic factors in this disease are not known. The objectives of this proposal are to determine if hereditary susceptibility predisposes African Americans to sarcoidosis and to identify sarcoidosis susceptibility genes in African Americans. The study will be carried out in African American families ascertained through 400 African American sarcoidosis patients evaluated at the Henry Ford Health System. They plan to test for association of sarcoidosis with markers for candidate genes using the affected family-based control method and test for possible environmental risk factors and genetic mechanisms of disease transmission by performing a segregation analysis in African American families. If one or more of the candidate genes studied show a strong association with sarcoidosis or if there is an indication of major gene segregation for the disease, they will be well positioned for future linkage studies. Investigating the hereditary susceptibility of sarcoidosis can best be done in African Americans, because of the greater severity and occurrence of disease in this population. Once the reasons for familial aggregation of sarcoidosis are determined, the investigators state that the etiology of this disease will be better understood and suitable prevention and treatment should be able to be designed.